1.1.2 Vector quantities have magnitude and an associated direction. A
vector quantity may be represented by an arrow. The length of the
arrow represents the magnitude, and the direction of the arrow the
direction of the vector quantity.
2 Contact and non-contact forces
2.1 contact forces – the
objects are physically
touching
2.1.1 friction, air resistance,
tension and normal contact
force.
2.2 non-contact forces – the
objects are physically
separated.
2.2.1 non-contact forces are
gravitational force,
electrostatic force and
magnetic force.
2.3 Force is a vector
quantity
3 Gravity
3.1 Weight is the force acting on an
object due to gravity. The force of
gravity close to the Earth is due to
the gravitational field around the
Earth.
3.1.1 The weight of an object depends on the
gravitational field strength at the point
where the object is.
4 Resultant forces
4.1 A number of forces acting on an
object may be replaced by a single
force that has the same effect as all
the original forces acting together.
This single force is called the
resultant force.
4.2 A single force can be
resolved into two
components acting at right
angles to each other.
4.2.1 The two component forces together
have the same effect as the single force.
5 Moments, levers and gears
5.1 A force or a system of
forces may cause an
object to rotate.
5.2 If an object is balanced,
the total clockwise
moment about a pivot
equals the total
anticlockwise moment
about that pivot.
5.3 A simple lever and a simple gear
system can both be used to
transmit the rotational effects of
forces.
6 Pressure and pressure differences in fluids
6.1 Pressure in a fluid 1
6.1.1 pressure = force normal to a surface/area
of that surface {p = F/A} pressure, p, in
pascals, Pa force, F, in newtons, N area, A,
in metres squared, m^2
6.1.2 The pressure in fluids
causes a force normal (at
right angles) to any
surface.
6.2 Pressure in a fluid 2
6.2.1 pressure = height of the column × density of the liquid ×
gravitational field strength [ p = h ρ g ] pressure, p, in pascals,
Pa height of the column, h, in metres, m density, ρ, in
kilograms per metre cubed, kg/m^3 gravitational field strength,
g, in newtons per kilogram, N/kg (In any calculation the value
of the gravitational field strength (g)
6.2.1.1 The more dense a given liquid is, the more particles it has a
certain space. This means there are more particles that are
able to collide so that pressure is higher . As the depth of the
liquid increases, the number of particles above that point
increases. The weight of these particles adds to the pressure
felt at that point, so liquid pressure increases the depth.
6.3 Atmospheric
pressure
6.3.1 The atmosphere is a thin layer (relative to the
size of the Earth) of air round the Earth. The
atmosphere gets less dense with increasing
altitude. Air molecules colliding with a surface
create atmospheric pressure. The number of
air molecules (and so the weight of air) above a
surface decreases as the height of the surface
above ground level increases. So as height
increases there is always less air above a
surface than there is at a lower height. So
atmospheric pressure decreases with an
increase in height
6.3.2 As the altitude increases, atmospheric
pressure decreases
6.3.2.1 This is because the altitude increases, the atmosphere gets less
dense , so there are fewer air molecules that are able to colide
with the surface.
6.3.2.1.1 There are also fewer air molecules above a surface
as the height increases . this means tht the weight
of the air above it, which contributes to the
atmospheric pressure, decreases with altitude
7 Distance and displacement
7.1 Distance is how far an object moves. Distance does not involve
direction. Distance is a scalar quantity. Displacement includes both
the distance an object moves, measured in a straight line from the
start point to the finish point and the direction of that straight line.
Displacement is a vector quantity.
8 Speed
8.1 Speed does not involve direction. Speed is a scalar
quantity. The speed of a moving object is rarely constant.
When people walk, run or travel in a car their speed is
constantly changing.
8.1.1 It is not only moving objects that have varying
speed. The speed of sound and the speed of the
wind also vary. A typical value for the speed of
sound in air is 330 m/s.
8.1.1.1 distance travelled = speed × time [s = v t] distance, s, in
metres, m speed, v, in metres per second, m/s time, t, in
seconds, s
9 Velocity
9.1 The velocity of an object is its speed in a given
direction. Velocity is a vector quantity.
9.1.1 As an object is moving in a circle
at a constant seed has a changing
velocity as the direction is always
changing e.g a car gong around a
roundabout .
10 The distance–time
relationship
10.1 If an object moves along a straight line, the distance travelled
can be represented by a distance–time graph. The speed of an
object can be calculated from the gradient of its distance–time
graph.
10.1.1 If an object is accelerating, its speed at any particular time can be
determined by drawing a tangent and measuring the gradient of
the distance–time graph at that time.
11 Acceleration
11.1 acceleration = change in
velocity /time taken (a = ∆
v/t) acceleration, a, in
metres per second
squared, m/s^2 change in
velocity, ∆v, in metres per
second, m/s time, t, in
seconds, s
11.1.1 The acceleration of an object can be
calculated from the gradient of a
velocity–time graph.
11.1.1.1 Near the Earth’s surface any object
falling freely under gravity has an
acceleration of about 9.8 m/s2 .
11.1.1.2 An object falling through a
fluid initially accelerates
due to the force of gravity.
Eventually the resultant
force will be zero and the
object will move at its
terminal velocity.
11.1.1.2.1 When falling objects first sett off, the force of gravity is much
more that the frictional force slowing them down. As the speed
increases the friction builds up. This gradually reduces the
acceleration until eventually the frictional force is equal to the
accelerting force. It will have reached its maximum speed or
terminal velocity and will fall at a steady speed.
11.1.1.2.1.1 Terminal velocity depends on the objects shape and area
11.2 An object that slows down is
decelerating
11.3 The distance travelled by an
object (or displacement of an
object) can be calculated
from the area under a
velocity–time graph.
11.4 The following equation applies to uniform
acceleration: (final velocity)^ 2 − (initial
velocity )^2 = 2 × acceleration × distance.{
v^2 − u^2 = 2 a s } final velocity, v, in
metres per second, m/s initial velocity, u,
in metres per second, m/s acceleration, a,
in metres per second squared, m/s^2
distance, s, in metres, m
12 Newtons first law
12.1 Newton’s First Law: If the resultant force
acting on an object is zero and: • the object is
stationary, the object remains stationary •
the object is moving, the object continues to
move at the same speed and in the same
direction. So the object continues to move at
the same velocity
12.1.1 So, when a vehicle travels at a steady
speed the resistive forces balance the
driving force.
12.1.1.1 So, the velocity (speed and/or
direction) of an object will only
change if a resultant force is acting on
the object.
13 Newtons second law
13.1 The acceleration of an object
is proportional to the
resultant force acting on the
object, and inversely
proportional to the mass of
the object.
13.1.1 resultant force = mass ×
acceleration F = m a force, F,
in newtons, N mass, m, in
kilograms, kg acceleration,
a, in metres per second
squared, m/s2
13.1.1.1 Required practical activity 7: investigate the
effect of varying the force on the acceleration
of an object of constant mass, and the effect of
varying the mass of an object on the
acceleration produced by a constant force.
14 Newtons third law
14.1 Newton’s Third Law: Whenever two
objects interact, the forces they exert
on each other are equal and opposite.
15 Stopping distance
15.1 The stopping distance of a vehicle is the sum of the distance the
vehicle travels during the driver’s reaction time (thinking
distance) and the distance it travels under the braking force
(braking distance). For a given braking force the greater the
speed of the vehicle, the greater the stopping distance.
15.1.1 Factors affecting braking distance
1:The braking distance of a vehicle
can be affected by adverse road
and weather conditions and poor
condition of the vehicle. Adverse
road conditions include wet or icy
conditions. Poor condition of
the vehicle is limited to the
vehicle’s brakes or tyres.
15.1.2 Factors affecting braking distance 2:When a force is
applied to the brakes of a vehicle, work done by the
friction force between the brakes and the wheel
reduces the kinetic energy of the vehicle and the
temperature of the brakes increases. The greater the
speed of a vehicle the greater the braking force
needed to stop the vehicle in a certain distance. The
greater the braking force the greater the deceleration
of the vehicle. Large decelerations may lead to brakes
overheating and/or loss of control.
16 Momentum
16.1 momentum = mass × velocity {p = m v} momentum, p, in
kilograms metre per second, kg m/s mass, m, in kilograms,
kg velocity, v, in metres per second, m/s
16.2 Conservation of momentum
16.2.1 In a closed system, the total momentum
before an event is equal to the total
momentum after the event. This is called
conservation of momentum.
16.3 Changes in momentum
16.3.1 The equations F = m × a and a = v − u/ t combine to give the
equation F = m ∆ v/ ∆ t where m∆v = change in momentum ie
force equals the rate of change of momentum.